In a sauté pan over medium heat, melt the butter. Add the onion and cook until soft, about 10 minutes. Transfer the onion to a slow cooker. Add the squash puree, apple, stock, bay leaves and the 3 tsp. salt to the slow cooker and stir to combine. Cover and cook for 2 hours according to the manufacturers instructions.

Remove the bay leaves and discard. Add the crème fraîche. Using a stick blender, puree the soup directly in the slow cooker until smooth. Stir in the coriander and ginger. Ladle the soup into warmed soup bowls and season the slices with salt and pepper. Serve immediately.